My two cents:
Elvis Andrus is a career 84 OPS+ in 5 full seasons. Kemp is a career 126 OPS+.
In other words, Andrus is a terrible hitter. Not mediocre, not below average. Terrible. He does make up for it defensively, and thus you can semi-live with a bad hitting shortstop who is a good defender. And yes, he steals bases which slightly mitigates the lack of hitting. In a vacuum he is okay as your shortstop.
However, if you have a replacement for him in the organization - and this is without taking any possible trades into account - you replace him. He should be the type of guy you are constantly attempting to upgrade. If you have a potential young all-star waiting behind him, it should be a no-brainer. You play Profar, you figure out what to do with Andrus, not the other way around.
As far as the trade, keep in mind, as well as being a far superior hitter, Kemp stole 40 bases in his last full season. I get the issue with the contract; if the organization doesn't have money to burn, you have to be careful that the players you pay 20 million a year are actually on the field. If the Rangers have a limited payroll, it's a big risk. It would hurt the organization really badly if they are paying Kemp 20 mil a year for 5 or 6 years or whatever it is and he is injured all the time. I'm not sure I'd do it if I were the Rangers.
But taking the money out of it, Kemp for Andrus is an easy decision. I can't actually imagine that the Dodgers would do it.